μ-XRF/μ-RS vs. SR μ-XRD for pigment identification in illuminated manuscripts

For the non-destructive identification of pigments and colorants in works of art, in archaeological and in forensic materials, a wide range of analytical techniques can be used. Bearing in mind that every method holds particular limitations, two complementary spectroscopic techniques, namely confocal μ-Raman spectroscopy (μ-RS) and μ-X-ray fluorescence spectroscopy (μ-XRF), were joined in one instrument. The combined μ-XRF and μ-RS device, called PRAXIS unites both complementary techniques in one mobile setup, which allows μ- and in situ analysis. μ-XRF allows one to collect elemental and spatially-resolved information in a non-destructive way on major and minor constituents of a variety of materials. However, the main disadvantages of μ-XRF are the penetration depth of the X-rays and the fact that only elements and not specific molecular combinations of elements can be detected. As a result μ-XRF is often not specific enough to identify the pigments within complex mixtures. Confocal Raman microscopy (μ-RS) can offer a surplus as molecular information can be obtained from single pigment grains. However, in some cases the presence of a strong fluorescence background limits the applicability. In this paper, the concrete analytical possibilities of the combined PRAXIS device are evaluated by comparing the results on an illuminated sheet of parchment with the analytical information supplied by synchrotron radiation μ-X-ray diffraction (SR μ-XRD), a highly specific technique. PACS  33.20.Fb; 61.05.cp; 33.20.Rm; 07.85.Qe; 91.65.An     

Cultural heritage and archaeology materials studied by synchrotron spectroscopy and imaging

The use of synchrotron radiation techniques to study cultural heritage and archaeological materials has undergone a steep increase over the past 10–15 years. The range of materials studied is very broad and encompasses painting materials, stone, glass, ceramics, metals, cellulosic and wooden materials, and a cluster of organic-based materials, in phase with the diversity observed at archaeological sites, museums, historical buildings, etc. Main areas of investigation are: (1) the study of the alteration and corrosion processes, for which the unique non-destructive speciation capabilities of X-ray absorption have proved very beneficial, (2) the understanding of the technologies and identification of the raw materials used to produce archaeological artefacts and art objects and, to a lesser extent, (3) the investigation of current or novel stabilisation, conservation and restoration practices. In terms of the synchrotron methods used, the main focus so far has been on X-ray techniques, primarily X-ray fluorescence, absorption and diffraction, and Fourier-transform infrared spectroscopy. We review here the use of these techniques from recent works published in the field demonstrating the breadth of applications and future potential offered by third generation synchrotron techniques. New developments in imaging and advanced spectroscopy, included in the UV/visible and IR ranges, could even broaden the variety of materials studied, in particular by fostering more studies on organic and complex organic–inorganic mixtures, while new support activities at synchrotron facilities might facilitate transfer of knowledge between synchrotron specialists and users from archaeology and cultural heritage sciences.     

稀土原子与离子的自然辐射寿命测量

概述了当前自由原子和离子的激发态自然辐射寿命测量技术的进展。以LaⅠ和PrⅡ为例,系统介绍了几种稀土元素自由原子和离子激发态寿命测量技术并分析了它们的优缺点;以SmⅡ为例,详细介绍了激光烧蚀产生自由原子(离子)技术及结合激光诱导荧光时间分辨光谱技术进行激发态寿命测量的优缺点。最后,探讨了改进上述技术局限性的解决思路,以期进一步提高辐射寿命测量的精确度。     

Monitoring insect pest infestation via different spectroscopic techniques

Nowadays, monitoring and observing insect pest populations is a major and crucial issue in agriculture, especially for crop protection. Spectroscopic techniques are well recognized for detecting and monitoring insect pests in the field and also the internal quality of fruit. There are several spectroscopic techniques with specific characteristic features, including mass spectrometry, ultraviolet–visible spectroscopy, infrared spectroscopy, and nuclear resonance spectroscopy. Nevertheless, limitations and complexity are the constraints of these technologies. In this paper, the spectroscopic and imaging spectroscopic techniques are discussed, compared, and investigated, namely fluorescence light detection and ranging (LIDAR) to study the fluorescence of diverse types of planthopper (Hemiptera) and moth (Lepidoptera), visible and near-infrared (Vis/NIR) spectroscopy to detect internal insect-infested jujubes, NIR spectroscopy to determine spectral properties of oil palm bagworms, hyperspectral transmittance image for detecting insect-damaged vegetable soybeans, and remote sensing measurement to detect bagworm infestation in oil palm plantations. These techniques are found to be reliable methods for better monitoring of insect pest movement in the harvested plant and in the ground, for the detection of insect-damaged vegetable soybeans and internal insect infestation in jujubes, and for the determination of oil palm bagworm spectral properties.     

Measurement of water film thickness by laser-induced fluorescence and Raman imaging

We present two non-intrusive, laser-based imaging techniques for the quantitative measurement of water fluid film thickness. The diagnostics methods are based on laser-induced fluorescence (LIF) of the organic tracer ethyl acetoacetate added to the liquid in sub-percent (by mass) concentration levels, and on spontaneous Raman scattering of liquid water, respectively, both with excitation at 266 nm. Signal intensities were calibrated with measurements on liquid layers of known thickness in a range between 0 and 500 μm. Detection via an image doubler and appropriate filtering in both light paths enabled the simultaneous detection of two-dimensional liquid film thickness information from both methods. The thickness of water films on transparent quartz glass plates was determined with an accuracy of 9% for the tracer LIF and 15% for the Raman scattering technique, respectively. The combined LIF/Raman measurements also revealed a preferential evaporation of the current tracer during the time-resolved recording of film evaporation.     

Analytical Methods for the Characterization of Organic Dyes in Artworks and in Historical Textiles

Abstract

Dyes are among the most significant components in works of art and archaeological findings. In the scientific examination of historical artefacts, the identification of natural dyestuffs is a challenging task, due to the complexity of their chemical composition and the possible presence of mixtures of chromophores and degradation products. For this reason, in the last few decades, new analytical procedures and techniques have been developed and improved for the characterization of organic dyes and their identification in microsamples. This review looks at the chemical composition of natural organic dyeing materials used in the field of the cultural heritage and focuses on several analytical methods based on spectrometric and chromatographic techniques that have contributed to the study of organic dyes in works of art and archaeological findings.     

Vibrational and electronic properties of painting lakes

Naturally occurring dyes have been used to produce painting pigments, called lakes, by precipitation or adsorption of an organic dyestuff onto an insoluble inorganic substrate. Most natural dyes link to metal cations, by means of coordination bonds. The stable complexes formed precipitate together with solid amorphous hydrous aluminum oxide in alkaline solutions, yielding a hybrid material called a lake. Conventional chromatographic methods for lake analysis require dye extraction from the substrate; as a consequence, they do not provide any information about the organo-metallic complexes. In this work a comprehensive investigation based on X-ray fluorescence, Fourier transform infrared and UV–visible absorption and emission spectroscopies was carried out on 13 organic pigments derived from eight different natural sources. Three different kinds of substrate containing aluminum hydroxide were distinguished dependent on different preparation procedures. Information concerning the recipe and the dye composition was obtained by UV–visible spectroscopies. Dyes from different sources (animal or vegetal) could be distinguished. This study shows that the combined use of different spectroscopic techniques provides complementary information to high-performance liquid chromatography and therefore can be proposed for a molecular non-invasive investigation of these materials on works of art. PACS  87.64.Ni; 87.64.Je     

Radiative lifetimes of highly excited odd-parity levels of neutral lanthanum

New radiative lifetimes of 24 high-lying odd-parity levels of neutral lanthanum are reported using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy. The investigated levels ranging from 34 213 to 40 910 cm^-1 were excited from the ground or metastable states using one-photon excitation. La atoms are produced by laser ablation on a solid La sample. The lifetimes were evaluated from transient LIF signals detected with a fast detection system. The obtained lifetime results, generally with uncertainties less than  ±7%, are in the range from 15.7 to 121 ns.     

Emerging biomedical and advanced applications of time-resolved fluorescence spectroscopy

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods, are resulting in the rapid migration of timeresolved fluorescence to the clinical chemistry lab, the patient's bedside, and even to the doctor's office and home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. Future horizons of state-of-the-art spectroscopy are also described. Two photon-induced fluorescence provides an increased information content to time-resolved data. Two photoninduced fluorescence, combined with fluorescence microscopy and time-resolved imaging, promises to provide detailed three-dimensional chemical imaging of cells. Additionally, it has recently been demonstrated that the pulses from modern picosecond lasers can be used to quench and/or modify the excited-state population by stimulated emission since the stimulated photons are directed along the quenching beam and are not observed. The phenomenon of light quenching should allow a new class of multipulse time-resolved fluorescence experiments, in which the excited-state population is modified by additional pulses to provide highly oriented systems.     

Ultra-fast spectroscopy and extreme nonlinear optics by few-optical-cycle laser pulses

Many fundamental processes of radiation–matter interaction, which take place on the ultra-short time scale, can now be directly investigated by using few-optical-cycles light pulses with duration <10 fs. We discuss two techniques for generating such pulses: broad-band parametric amplification, which allows the generation of pulses in the visible range suitable for spectroscopy, and compression of high-energy light pulses in a hollow fiber. As an example of application in time-resolved spectroscopy we report results of pump–probe experiments in a prototypical conjugated molecule, namely sexithiophene. The new laser sources, due to their characteristics of peak power and coherence, also allow the exploration of new fields of experimental physics, such as extreme nonlinear optics. We focus on high-order harmonics, showing that a high-energy bunch of photons, up to the X-ray-energy region, with coherence typical of laser radiation and time duration comparable to or shorter than the exciting pulses, can be generated. Received: 31 July 2000 / Revised version: 19 September 2000 / Published online: 8 November 2000     

A UV–Visible–NIR fluorescence lifetime imaging microscope for laser-based biological sensing with picosecond resolution

This article describes the design and characterization of a wide-field, time-domain fluorescence lifetime imaging microscopy (FLIM) system developed for picosecond time-resolved biological imaging. The system consists of a nitrogen-pumped dye laser for UV–visible–NIR excitation (337.1–960 nm), an epi-illuminated microscope with UV compatible optics, and a time-gated intensified CCD camera with an adjustable gate width (200 ps-10^-3 s) for temporally resolved, single-photon detection of fluorescence decays with 9.6-bit intensity resolution and 1.4-μm spatial resolution. Intensity measurements used for fluorescence decay calculations are reproducible to within 2%, achieved by synchronizing the ICCD gate delay to the excitation laser pulse via a constant fraction optical discriminator and picosecond delay card. A self-consistent FLIM system response model is presented, allowing for fluorescence lifetimes (0.6 ns) significantly smaller than the FLIM system response (1.14 ns) to be determined to 3% of independently determined values. The FLIM system was able to discriminate fluorescence lifetime differences of at least 50 ps. The spectral tunability and large temporal dynamic range of the system are demonstrated by imaging in living human cells: UV-excited endogenous fluorescence from metabolic cofactors (lifetime ∼1.4 ns); and 460-nm excited fluorescence from an exogenous oxygen-quenched ruthenium dye (lifetime ∼400 ns). Received: 23 February 2003 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-734/9361-905, E-mail: mycek@umich.edu     

Lasers as Light Sources for Analytical Atomic Spectrometry

Abstract

Lasers have advantages compared to conventional light sources, which include high power, a monochromatic emission profile, stability, and rapid tuning across an atomic line. These advantages have resulted in superior analytical figures of merit and methods of background correction compared to conventional light sources. The most widely used lasers for atomic spectrometry include dye laser systems, optical parametric oscillator systems, and diode lasers. Three principal techniques employ lasers as light sources. Laser‐excited atomic fluorescence spectrometry (LEAFS) involves the use of laser light to excite atoms that emit fluorescence and serves as the analytical signal. Laser‐enhanced ionization (LEI) involves laser excitation of atoms to an excited state energy level at which collisional ionization occurs at a higher rate than from the ground state. Diode laser atomic absorption spectrometry (DLAAS) employs a DL as a source to excite atoms in an atom cell from the ground state to an excited state. The analytical signal is involves the ratio of the incident and transmitted beams. Recent applications of these techniques are discussed, including practical applications, hyphenated techniques employing laser‐induced plasmas, and work to characterize fundamental spectroscopic parameters.     

Acetylene-Substituted Two-Photon Absorbing Molecules With Rigid Elongated Pi-Conjugation: Synthesis,Spectroscopic Properties and Two-Photon Fluorescence Cell Imaging Applications

Two asymmetrical molecules with substituted acetylene as central rigid elongated conjugation are reported as potential chromophores for two-photon microscopic imaging. These molecules consist of a typical D–π–A structure, have different donors (D), the same π-conjugated center (π) and the same acceptor (A). Structural characterization and spectroscopic properties, including single-photon (linear) absorption, quantum yields, single-photon fluorescence, and two-photon absorption spectra, were studied in solvents with different polarity. These acetylene-substituted molecules were found to have high two-photon absorption cross-sections (for example, 690 GM for molecule 1 in toluene), which were determined by a two-photon induced fluorescence method using a femtosecond Ti: sapphire laser as excitation source. Single- and two-photon cellular imaging experiments demonstrate that the substituted acetylene derivatives could be one kind of promising two-photon fluorescence probes for cellular imaging.     

Multi-photon excitation fluorescence and third-harmonic generation microscopy measurements combined with confocal Raman microscopy for the analysis of layered samples of varnished oil films

The non-destructive determination of layer structures in works of art remains a significant challenge. Non-linear microscopy and confocal Raman microscopy (CRM) were employed for characterisation of varnish-media layers in model samples, providing important information regarding the thickness of materials and the identification of different media in depth. Commonly found triterpenoid varnishes mastic and dammar were applied over a single layer of films of linseed oil. Non-linear microscopy of samples was carried out using a 1028-nm femtosecond laser source; both third-harmonic generation signals (THG) and three-photon fluorescence signals (3PEF) of samples were collected in an effort to measure the thickness of mono- and bi-layers; in parallel scans of larger areas were undertaken to assess heterogeneities in samples with spatial resolution of ∼2 μm. Complementary spectroscopic information from CRM collected with both a 514.5-nm argon-ion and a 785-nm diode lasers coupled with a 100X objective and a motorised stage was carried out. Comparison of C–H stretching regions of Raman spectra allowed the differentiation between different molecular materials and the fingerprint region was employed for the depth profiling of the samples.     

The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Attenuation corrections for in-cylinder NO LIF measurements in a heavy-duty Diesel engine

Quantification of the nitric oxide (NO) concentration inside the cylinder of a Diesel engine by means of laser-induced fluorescence (LIF) measurements requires, amongst others, knowledge of the attenuation of the ultraviolet radiation involved. We present a number of laser diagnostic techniques to assess this attenuation, enabling a correction for laser intensity and detection efficiency of the raw NO LIF data. Methods discussed include overall laser beam transmission, bidirectional laser scattering (bidirectional LIF), spectrally resolved fluorescence imaging, and Raman scattering by N₂. A combination of techniques is necessary to obtain the complete attenuation of laser beam and NO fluorescence. The overall laser beam transmission measurements and bidirectional LIF measurements (the latter yielding spatially resolved transmission) provide evidence of a non-uniform attenuation distribution, with predominant attenuation within or near the piston bowl. Fluorescence imaging of multiple vibrational bands through a spectrograph is shown to be a powerful method for obtaining spatially resolved data on the transmission losses of fluorescence. Special attention is paid to the role of CO₂ and O₂ as UV light absorbers, and the consequences to different excitation-detection schemes for NO. PACS 82.33.Vx; 42.62.Fi; 33.20.t     

Characterization of pigments used in painting by means of laser-induced plasma and attenuated total reflectance FTIR spectroscopy

The study of pigments which are found in the works of art is one of the most important tasks in the examination of historic, artistic and archaeological materials since it can provide information about their source, the pictorial technique used or the presence of restoration works.In some studies, the historical, artistic and technical characterization of the artefact is not the final goal but its restoration. In those cases, the knowledge about the chemical composition inferred from the analysis of the artwork is crucial for conservators and restorers in order to ensure that the same pigments that were used in the original work are employed for the restoration.In this work, the analytical characterization of a range of different pigments commonly used in art has been carried out using laser-induced plasma (LIBS) and attenuated total reflectance (ATR)-FTIR spectroscopy. The main purpose of this study is to provide a preliminary database of LIBS and ATR-FTIR spectra in order to supply both elemental and molecular information, respectively.     

A deep view in cultural heritage—confocal micro X-ray spectroscopy for depth resolved elemental analysis

Quantitative X-ray fluorescence (XRF) and particle induced X-ray emission (PIXE) techniques have been developed mostly for the elemental analysis of homogeneous bulk or very simple layered materials. Further on, the microprobe version of both techniques is applied for 2D elemental mapping of surface heterogeneities. At typical XRF/PIXE fixed geometries and exciting energies (15–25 keV and 2–3 MeV, respectively), the analytical signal (characteristic X-ray radiation) emanates from a variable but rather extended depth within the analyzed material, according to the exciting probe energy, set-up geometry, specimen matrix composition and analyte. Consequently, the in-depth resolution offered by XRF and PIXE techniques is rather limited for the characterization of materials with micrometer-scale stratigraphy or 3D heterogeneous structures. This difficulty has been over-passed to some extent in the case of an X-ray or charged particle microprobe by creating the so-called confocal geometry. The field of view of the X-ray spectrometer is spatially restricted by a polycapillary X-ray lens within a sensitive microvolume formed by the two inter-sectioned focal regions. The precise scanning of the analyzed specimen through the confocal microvolume results in depth-sensitive measurements, whereas the additional 2D scanning microprobe possibilities render to element-specific 3D spatial resolution (3D micro-XRF and 3D micro-PIXE). These developments have contributed since 2003 to a variety of fields of applications in environmental, material and life sciences. In contrast to other elemental imaging methods, no size restriction of the objects investigated and the non-destructive character of analysis have been found indispensable for cultural heritage (CH) related applications. The review presents a summary of the experimental set-up developments at synchrotron radiation beamlines, particle accelerators and desktop spectrometers that have driven methodological developments and applications of confocal X-ray microscopy including depth profiling speciation studies by means of confocal X-ray absorption near edge structure (XANES) spectroscopy. The solid mathematical formulation developed for the quantitative in-depth elemental analysis of stratified materials is exemplified and depth profile reconstruction techniques are discussed. Selected CH applications related to the characterization of painted layers from paintings and decorated artifacts (enamels, glasses and ceramics), but also from the study of corrosion and patina layers in glass and metals, respectively, are presented. The analytical capabilities, limitations and future perspectives of the two variants of the confocal micro X-ray spectroscopy, 3D micro-XRF and 3D micro-PIXE, with respect to CH applications are critically assessed and discussed.     

Laser ablation of phenylazide in an argon matrix: direct observation and chemical reactivity of ablated fragments

Ablation of pentafluorophenylazide (FPA) in an Ar matrix at 8–10 K was carried out upon irradiation with ns-pulsed UV lasers in a vacuum. The plume of ablated products was monitored by a time-resolved imaging/spectroscopic technique using a gated and intensified CCD camera system. A large amount of pentafluorophenylnitrene (FPN) having a high kinetic energy (≈6 eV) was ejected as fragments from the matrix film during ablation. A quantitative formation of triplet FPN from the photolysis of the FPA was observed by spectroscopic measurements in the IR and UV-visible regions, and was confirmed by a theoretical IR spectrum calculated according to density functional theory. A FPN beam is useful for chemical surface modification of organic materials, such as aromatic polyester and alkylthiol. A surface analysis of these materials by X-ray photoelectron spectroscopy and Fourier transform infrared reflection absorption spectroscopy showed that the FPN was immobilized onto the surface through chemical bonds. This technique for the chemical surface modification of materials is made possible by a pulsed beam of reactive fragments with a high density in the laser ablation process. Received: 14 June 1999 / Accepted: 18 June 1999 / Published online: 21 October 1999